I purchased two DQ542MA drivers in order to run two NEMA 17 steppers. After about five days of use I noticed that the green indicator light had gone out on both drivers.

The DQ542MA driver running my NEMA 23 High Torque stepper was still running and it has been connected to that stepper for five months now. Using an Ohm meter to check I found that the 10amp 125v LittleFuse connected to the power pins had blown on both drivers connected to the NEMA 17 steppers cutting off the power.

I decided to test the still working driver by disconnecting it from the NEMA 23 stepper and corresponding pins on the motherboard and connecting and resetting it to work with one of the NEMA 17 steppers. The minute I turned my printer back on, the still working stepper (now attached to the NEMA 17 stepper) immediately blew the same fuse. I don't understand why the NEMA 17 steppers blew the fuses of the drivers, seeing as how both are properly set to a RMS of 1.69 and a pulse/rev of 400, and both are connected to a 24v PSU.

My question is: "When I fix the drivers should I solder in a 15amp 125v LittleFuse to better help the power flow and prevent any further blown fuses?"

  • $\begingroup$ Did you try to change the motors instead ? What are the rating for your NEMA 17's ? ( Sadly you blew all your drivers .) Check your motors first always . I don't see any logic in having a higher amp fuse . it should never consume that much current if the steppers current rating is less than fuse's current rating . My best suggestion is to solder back the 10 A 125 V fuse and get a driver working again and make sure your motor is not short circuiting . Tell me what happens . I wanna use the same drivers next month . $\endgroup$ Jun 26 '18 at 10:53
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    $\begingroup$ Instead of replacing the 10A fuse with a 15A fuse, consider replacing it with a wire link. Wires are much more reliable than fuses, because they don't blow as easily. In fact, it would be a good idea to replace all fuses with wire links, because then we'd never have to replace a blown fuse ever again! $\endgroup$ Jun 26 '18 at 12:38
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    $\begingroup$ @TomvanderZanden a master of irony for you! $\endgroup$
    – profesor79
    Jun 26 '18 at 14:20
  • $\begingroup$ @AxelFernandes - Don't you mean solder back the 10 A 125 V fuse? Upgrading the current capacity of a fuse in a device designed and built to specific tolerances is generally a very dangerous thing to do (as Professor's answer points out) unless you really know what you are doing... Your comment, whilst well meaning, just seems to be particularly bad, if not hazardous, advice. $\endgroup$
    – Greenonline
    Jun 27 '18 at 0:49
  • $\begingroup$ @Greenonline sorry i was just brain storming its not an answer lol . Also yes your right i did mean solder back the fuse i forgot to mention the correct ratings . :P $\endgroup$ Jun 27 '18 at 3:49

If the fuse blows - there is a reason for that, so changing it for a higher rating without understanding the source of the problem is:

Asking for fire!!!

Every stepper has its own internal resistance (and as we have a magnetic field it is called a reluctance), that is limiting the max current, but this equation needs to take U given to the motor.

A simple and popular solution is to give only as much voltage as needed, utilizing the resistance (RL) of the winding to limit the current (fig. 4a). A more complicated but also more efficient and precise solution is the inclusion of a current generator (fig. 4b), to achieve independence from the winding resistance. The supply voltage in Fig. 4b has to be higher than the one in Fig. 4a. A comparison between both circuits in the dynamic load/working order shows visible differences.

Source Stepper motor driving by H. SAX - page 2

That said - the higher voltage applied to the stepper - the higher current is flowing via its coils.

Please check the datasheet of your driver to see how it is managing to current limit your stepper as that looks like a source of your issue.


Part Analysis

Let's see what we have:

  • The fuse in the driver is set to keep up the loads that the driver can safely handle.

  • The NEMA 17 results in a blown out fuse


The problem lies not in the driver, but the NEMA 17 motor or the wires to it and can be of several ways:

  • The motor has a short and is defective.
  • The motor is not rated to the driver board.
  • The wires to the motor create a short.

But there is also a 3rd option, as the driver board is connected to the controller:

  • The controller supplies the driver with too much current and fries it.


Do not solder in a higher rated fuse, as this is asking for fatal part failure - which could be fire just as much as totally frying the logic circuits on the board forever. Instead, find out what type of error resulted in the blown fuse, and replace these parts.


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